In biogas systems that particularly use the principle of dry fermentation, biomass is fermented within a box-shaped fermenter by means of percolation with a percolate such that biogas is produced. During this, the percolate as a rule is trapped and transferred into an external percolate container, from which the percolate in turn is recycled to the fermenter.
During this, it is important that the temperature of the substrate and/or of the percolate does not drop too much, since otherwise fermentation is inhibited. In known systems, however, heat loss plays a significant role.
To solve this problem, one may deal with heating of the percolate within the percolate tank, or with heating the substrate within the fermenter.
Both approaches require the provision of energy, such that conventional means are lacking in energy efficiency.